Abstract: In order to study the variation features of the free radical in the process of the coal low temperature oxidation, four different metamorphic degree coal sa mples were selected to the simulation experiments of the electron paramagnetic resonance and the risen temperature oxidation. The experiment results showed that the re were big differences in the free radical quantity and CO production value of coal with different metamorphic. The CO production value of the lignite was maximum an d the free radical concentration was minimum. The meager coal would be on the contrary. Thus the lower metamorphic degree of coal was, the less quantity of the free r adicals would be. In the oxidation process, the higher CO production was, the lower of the critical temperature would be and the easier of the spontaneous combustion w ould be occurred. Thus free radical concentration was found to be the index to judge the coal metamorphic degree and the oxidation progress. And the coal spontaneou s combustion oxidation process was revealed from the micro reaction.